Merge branch '69-add-compression-to-syntheses' into 'release-1.6'

Resolve "add compression to syntheses"

Closes #69 (closed)

See merge request !61 (merged)

(cherry picked from commit e34015cc)

3c3b599a add compression to snow annual map bd079a61 add compression to SMOD, SOD 02d3832b Update compute_NOBS.py